System and apparatus for controlling the supply of power to electric motors



March 11, 1952 E. w. JOHNSON 2,583,633

SYSTEM AND APPARATUS FOR CONTROLLING THE SUPPLY OF POWER TO ELECTRIC MOTORS Filed Sept. 21, 194% 2 SHEETS-SHEET 1 I I I 1 .l OURCE INVEN TOR. fie/V5.57 14/. Ja/m so v B March 11, 1952 JOHNSON 2,588,633

. W. SYSTEM AND APPARATUS FOR CONTROLLING THE SUPPLY OF POWER TO ELECTRIC MOTORS Filed Sept. 21, 1949 2 SHEETSSHEET 2 /0 I36 I J Yale/1W0 CONT/30L AMPL/F/EE fMIVJFORA/gg INVENTOR. gelvasr M Jmvsmv BY Aflorney Patented Mar. 11, 1952 SYSTEM AND APPARATUS FOR CONTROL- LING THE SUPPLY OF POWER TO ELEC- TRIC MOTORS Ernest W. Johnson, Everett, Mass.,

Transducer Corporation,

assignor to Boston, Mass.

Application September 21, 1949, Serial No. 117,025

6 Claims. (Cl. 318--207) This invention relates to circuits for controlling the power supplied to electric motors, and relates more particularly to circuits using relays for controlling the power supplied to remotely controlled electric motors of servo-mechanisms.

Relays are desirable for controlling the power supplied to electric motors in servo-mechanisms, since small error signals can control substantial amounts of power, but heretofore the controls using relays have had the disadvantages that the operation of the motors has not been smooth and accurate, and their speeds have not been controlled in even steps.

This invention provides smooth operation andevenly graduated speeds of the motors of servomechanisms. In one embodiment of the invention for controlling a two pole, two phase motor, a multiple contact relay is connected to each of the field windings, each relay including a, pluralityiof series connected resistors, some but not all of which are shorted out. Error voltages from a synchro-control transformer, together with reference voltage from a 60 cycle, alternating current source, are supplied into the input of a phase detector, the output of which is applied to the control grid of a control tube. The plate current of the control tube energizes solenoids for the two relays which cause one relay to increase the number of shorted out resistors in its associated field circuit, and which cause the other relay to simultaneously decrease the number of shorted out resistors in its associated field circuit. This causes the motor to rotate in one or the other direction depending upon the phase of the input voltages, and causes the motor to increase or decrease its speed in even steps.

In another embodiment of the invention, the error voltage from the synchro-control transformer is applied to one field winding of a two phase motor, and voltage from a 60 cycle, alternating current source is applied to the other field winding of the motor. The rotor of the motor rotates. brushes which wipe contacts connected to the junction points of series connected resistors which are connected to the field windings of a two phase motor which is to be controlled. Rotation of the brushes in one direction or the other causes the motor to be controlled to rotate in one direction or the other, and to change its speed depending upon the degree of rotation of the brushes. r An object of the invention is to provide smooth and uniform control of the speed of an electric motor. 7

Another object of the invention is to use-a cor 2 rection signal in a servo-mechanism to apply power to a remotely controlled motor in small, uniform steps. r

The invention will now be described with reference to the drawing, of which:

Fig. 1 is a circuit schematic illustrating one embodiment of the invention, and Y Fig. 2 is a circuit schematic illustrating another embodiment of the invention.

Referring first to Fig. 1 of the drawing, the conventional, sychro-control transformer Ill and the conventional, direct current, feed-back generator 9, have their outputs connected through the coupling capacitors II to the outer ends of the series connected potentiometers l2, one side of the output side of the transformer beingcom nected through the capacitor [3 to ground.

The sliders of the potentiometers l2 are connected through the resistors M to the control grids of the dual triode tube l5, the cathodes of which are grounded. One plate of the tube I5 is connected to one side of the transformer winding IS, the other side of which is connected through the resistor I! and the wiring l8 to a positive, direct current terminal of the power supply source IS. The resistor I! is also c0nnected through the resistor 20 to the other plate of the tube l5, which is connected through the capacitor 2!, the capacitor 22 shunted by the resistor 23, and the resistor 24 to the control grid of the control tube 24, which also is connected through the resistors 25 and 26 to a negative bias voltage connection within the source IS.

The transformer winding 26 which is induc tively coupled to the winding [5 which is shunted by the capacitor 21, is connected at its ends to the cathodes of the dual diode tube 28. The center point of the winding 26 is connected through the secondary winding of the transformer 29 to the junction point of the resistors 30 which are connected in series to the plates of the tube 28. A capacitor 3| is shunted across each resister 30. The primary winding of the transformer 29 is connected through the resistor 32 to cycle alternating current connections in the power source 19.

One plate of the tube 28 is connected to the wiring 33 leading to the negative bias terminal in the source l9, and its other plate is connected through the series connected resistors 34 to the junction point of the resistors 23 and 25 in the control grid circuit of the tube 24. The series connected capacitors 3B are connected to the outer ends of the resistors 34, and their junction point is connected through the resistor 31 shunted by the capacitor 38, to ground, and through the resistor 39 to the wiring 33.

The cathode and suppressor grid of the tube 24 are grounded. Its screen grid and plate are connected together and to the direct current, positive high voltage terminal of the source I9 through connections to be described in the following.

The circuit described so far is conventional. One side of the tube I5 amplifies the error voltages from the transformer I and supplys the amplified voltages to the phase detector tube28 to which the reference voltage from the transformer 29 is also supplied. The output of the phase detector tube 24 is applied to the control grid of the control tube 24 together with an amplified feedback signal from the other section of the tube I5, and which, as is well known, is for anti-hunt purposes, and which originates at the direct current generator 9 which is driven, as is conventional, by the servomotor to be controlled.

The plate resistance of the control tube 24 varies with variations in the voltages applied to its control grid, and is used to control'through the relays and 90, the direction of rotation of, and the speed of the motor 40 as will now'be described.

The motor '40 is a two pole, two phase motor having the field winding 4| connected at one "side to one side of the cycle source 42', and connected at its other side through the series connected resistors 43, 44, 45, 45, 41, 48, 49, 50, 5| and 52 to the other side of the source 42.

The other field winding 54 of the motor 40 is connected at one end to the source 42 at one side thereof, and is connected at its other end through the series connected resistors 55, 55, 51, 58,59, 50, 5|, 52, 53 and to the other side of the source '42.

The phase shift capacitor '55 is connected to the .field windings M and 54 of the motor 40.

The relay '55 has the contact 51 connected to the field winding 4|; has the armature 58 with the contact 59 connected to the junction point of the resistors with the contact H connected tothe junction point of the resistors 44 and 45; "has the armature 14 with the contact 15 connected to the junction point of the resistors 45 and 41; has the armature 15 with the contact 11 connected to the of the resistors 41and 48; has the armature 18 with the contact "19 connected to thejunction point of the resistors 48 and 49; has the armature with the contact 8| connected to the junction point or the resistors 49 and 50; has the armature 82 with the contact 83 connected to the junction point of the resistors 50 and 5|; has the armature 84 with the contact 85 connected to the junction point of the res'i'st'o'rs 5| and 52, and has the armature 85 conjunction point nected to the source 42.

The relay 55. has the plunger 81 of the sole noid 88 incontact with the underside of the armature 85. In its normal position as illustratedby Fig. 1 of the drawing, the plunger 81 has moved the armature 85 up against the contact 85 causing the armature 84 to be moved up against the contact 83, the armature 82 to be moved up against the contact 8|, the armature 80 to be moved up against the contact 19, and the armature 18 to be moved up against the contact 11. Thus, normally the resistors 48, 49, '50, 5], and 52 are shunted out of the "circuit of the field winding 4| of the motor 40.

The relay 90 has the contact 9| connected to 43 and 44; has the armature 10 sistors 50, 5|, 52,

the field winding 54 of the motor 40; has the armature 92 with the contact 93 connected to the junction point of the resistors 55 and 55; has the armature 94 with the contact 95 connected to the junction point of the resistors 55 and 51; has the armature 95 with the contact '91 connected to the junction point of the rethe armature I04 with the contact I05 connected to the junction point of the resistors 5| and 52;

has the armature I05 with the contact I01 connected to the junction point of the resistors 52 and 53; has the armature I08 with the contact I09 connected to the junction point of the resistors .53 and 54, and has the armature '||0 connected to the source 42.

The relay 90 has the plunger III of theisolenoid H2 in contact with the underside of the armature ||0. In its normal position as illustrated by Fig. l of the drawing, the plunger I II has moved the armature I I0 up against the contact I09 causing the armature I08 to be moved up against the contact I01, .the armature I05 to bemoved up against the contact I05,'the.arma'- ture I04 to be moved up against .the contact I93, and the armature I92. to be moved up against the contact IOI. Thus normally the .re-

53, and 54 are :shorted out of the-circuit of the field winding 540i the motor'Mi.

The solenoids 88 and M2, the potentiometers H5 and N5, the resistor I IB-and the control tube 24 are connected in a balanced bridge circuit to the positive, high voltage, direct connection in the powersource I9. Normally the same cur rent flows through both solenoids at which time there is no error voltage from the control transformer I0. The same number of resistors are in the circuits of the field windings 4| and 54 of the motor 40, resulting in equal currents through the field windings so the motor is at rest. I

If an error exists in one direction, the change in the bias on the control grid of the -'co'ntrol tube 24, and the resulting change in its plate resistance, will unbalance the bridge circuit 'in one direction causing the solenoid 88 to become more strongly energized and the solenoid -I'I2 to become less-strongly energized. The increased current through the solenoid 88 causes it toimove its plunger 81 further upwardly to cause "the armature 15 to touch the contact 15 and short out the resistor 41 from the field circuit of the winding 4.I of the motor 40. At the same "time the decreased current through the solenoid H2 permits the spring I-2I connected to the plunger III to move it downwardly causing the armature I02 to be spaced from the contact I01, and removing the short circuit from across the resistor 50, thus connecting this resistor in the circuit of the field winding 54 of the motor 40.

'The removal of theres'istor 41 from the'circult of the field winding 4|, and the connection :or the resistor 50 in the circuit of the field winding 54, will cause, without changing the current drawn by the motor 40, the field winding 4| to become more strongly energized and the :field windin'g'54 to become less strongly energized, and will cause the motor to rotate in a direction to correct the error.

-Further increases in error in the same direction will cause the solenoid 88 to become still more strongly energized, and the solenoid NZ to become still less strongly'energized, and cause theirplungers to short out other resistors in the circuit of the field winding 4|, and to remove the shorts from across other resistors in the circuit of the field winding 54, causing the motor 40 to speed up in proportion to the degree of error.

As the error decreases towards zero, the energizing currents of the solenoids will approach normal causing more resistance to be inserted in "the circuit'of the field winding 4|, and more resistance to be removed from the circuit of the field winding 54 until the motor 40 has rotated to correct the error.

Upon a reversal of error, the change in bias on the control gridof the control tube 24 will cause it to unbalance the bridge circuit in the other direction through its change in plate resistance, causing the solenoid 88 to become less strongly energized, and the solenoid II2 to become more strongly energized. This will cause the spring I20 connected to the plunger 81 to move it downwardly, and will cause the solenoid M2 to move the speed of the motor decreases in proportion.

Referring now to Fig. 2 of the drawing, the relay I25 corresponds to the relay 66 of Fig. l, and the relay I26 corresponds to the relay 90 of Fig. 1. ranged in a circular arc and connected to the junction points of the series .connected resistors 43 to 52 which are connected to the field winding 4| of the motor 40, and the end ones of which are connected to the outer ends of the end resistors 43 and 52. The contacts I2! are arranged to be wiped by the rotary brush I28.

The relay I25 has the contacts I29 arranged in a circular arc and connected to the junction points of the series connected resistors 55 to 64 which are connected to the field winding 54 of the motor 40, and the end ones of which are connected to the outer ends of the end resistors 53 and 64. The contacts I29 are arranged to be wiped by the rotary brush I30.

The brush I28 is connected to the outer end of the resistor 52, and when rotated in a clockwise direction it increases the number of resistors it shorts out, it normally shorting out one half of the resistors connected to the field winding 4|.

The brush I30 is connected to the outer end of the resistor 64, and when rotated in a clockwise direction it decreases the number of resistors it shorts out, it normally shorting out one half the resistors connected to the field winding 54.

The brushes I28 and I30 are connected through the linkage I 3| to the rotor of the'small, two pole, two phase, electric motor I32 which has one field winding I33 connected through the phase shifting capacitor I34 to the alternating current power source 42, and has the other field winding I35 connected through the amplifier I38 to the synchro-control transformer I0.

When the error is zero, the magnetic flux is established in the motor I32 by the field winding I33 alone so that no torque is produced in the motor. When an error exists. current flows in The'relay I25 has the contacts I2! ar the winding I35 so that a rotating flux is produced which drives the motor in a direction to correct the error. A reversal in the direction of the error causes the phase of the current inthe winding I35 to reverse, causing a reversal of the direction of rotation of the motor. V.

Rotation of the motor I32 in one direction causes the brushes I28 and I30 to rotate and to touch relay contacts which increase the number of resistors shorted out of the circuit of the field winding 4| by the relay I25, and which decrease the number of resistors shorted out of the circuit of the field winding 54 by the relay I26. This causes the field winding 4| to become more strongly energized than the field winding 54, and causes the motor 40 to rotate in a direction to correct the error.

Rotation of the motor in the other direction causes the brushes I28 and I30 to rotate in-.a direction to touch relay contacts which decrease the number of resistors shorted out of the circuit of the field winding 4| by the relay I25, and which increase the number of resistors shorted out of the circuit of the field winding 54 by the relay I26. This causes the field winding 54 to become more strongly energized than the. field winding 4|, causing the motor 40 to rotate in the opposite direction for correcting the error.

The spring I40 attached to the linkage I3I, serves to restore the relay brushes I28 and I30 to their normal positions when the error is reduced to zero. Y i ,w

The motor I32 thus functions as a phase detector in addition to rotating the brushes of the relays which control the power supplied to the motor 40. 1

The motor I32 instead of rotating contact wiping arms could instead, rotate cams which would replace the solenoids and their plungers illustrated by Fig. 1 of the drawing, for moving the relay armatures against their associated contacts.

Another advantage of this invention is that the power supplied to the remotely controlled motor can be independent of the power operating the other elements of a servo-mechanism. The servo amplifier design is determined only by the error sensing units employed and not by the power requirements of the servomotor. The output stage of the servo amplifier can be of the same design for any size servomotor.

While embodiments of the invention have been described for the purpose of illustration, it should be understood that the invention is not limited to the exact apparatus and arrangement of apparatus illustrated, since modifications thereof may be suggested by those skilled in the art, without departure from the essence of the invention.

What is claimed is:

1. A remote positioning system for an electric motor having a pair of windings for causing the rotor of the motor to rotate in opposite directions, comprising means including a first plurality of series connected resistors for energizing one of said windings, means including a second plurality of series connected resistors for energizing the other of said windings, resistor shorting means normally arranged to short out some but not all of the resistors of each of said pluralities of resistors, means for adjusting said shorting means for increasing the number of shorted out resistors in one of said pluralities and for simultaneously decreasing the number of shorted out resistors in the other of Said pluralities. a phase detector, means for supplying an awe- 8 error 'isignal to asaid detector, :and means includksaid. phase detector. for.;actuatingsaid means 'l'for'adjustingsaidshortingmeans.

2. A remote positioning system as claimed in claim 1 in which :the sresistorashortingimeans includes a pair of relays having contacts -convu'iected'to the junction points of the resistors,-and includes 'rsolenoid means for connecting and disconnecting. said contacts; :3. A remote positioning system -as-claimed in claimil in which the mesistorshOrti-ng means --in- :cludes contactsconnected to thehjunction points or the resistors, and includes rotary contact con- :nectir'ig and disconnecting means, "and in which the phase detector is an electric :motor which rotates-saidrotary means. i J

4. A remote positioning system-for'an electric motor; having :a pair ofwindings for causing' 'the rotor .of themotor to rotate in opposite direc- ,-tions,'comprising means including a firstflplurality of :series connected resistors for energizing one of said windings, means including a second iplurality :of series connected resistors for energizing the other of said windings, resistor shorting means normally arranged to short out somehut not allof the resistors of each of said pluralities of resistors, solenoid means for adjusting said shorting means to increase the'number of shorted out resistors in one of said pluralities, and to decrease thenumber of'shorted nut-resistors in the other of "said pluralities, -a phase detector, means for supplying an error in opposite directions, connected to said-rotary means :for rotating same, meanst-for supplying error signals into one of said last mentioned windings, and means for supplying a constant voltage and a reference voltage into the input ofzsa'iddetector and means connected to theout- :put of saiddetector .for energizing said solenoid i means.

--5. n remotepositioningsystem for an electric motor having a pair of windings for causing the rotor of the motor to rotate in opposite directions, comprising means including a :first plural- :ityofseries connectedresistors for energizing one of said windings, means including a secondpluralityof resistors for energizing the otherof said windings, resistor shorting means normally arranged to short out some but not all of the resistors in each of said .pluralities, said shorting means including contacts connected to the Junetion'ipoints of the resistors and including rotary means, an alternating current motor having a pair of windings :for causing itsrotorto'rotate frequency, constant voltage, alternating current into the other of said last'mentioned windings.

'6. A remote positioningsystem for an electric motor having a pair of windings for causing-the rotor of the-motor5-to rotate inopposite direcing aplurality-of series connected resistors connected to the other of :said windings for energizing same, contacts connected to --t he .i1;1nction .point's'oi the resistors of said first relax-other contacts connected to thejunction points of the resistors of said second relay, said relays having resistor shorting means normally arranged to short out some but not all of their-resistors, each shorting means including a solenoid 'and a contact member movable thereby for electrically connecting and-disconnecting its 'associatedcontacts, a phase detector, means for applying an error voltage and a reference voltage to the input 0f said detector, and means connected to the output of saiddetector for energizingone of said solenoids more strongly than the other solenoid when an error signal in i one direction isapplied to said detector, and 'for energizing the other of said solenoids more'strongly than said one solenoid when an error signal in the opposite direction is appliedto said detector.

ERNEST Wi-JOHNSGN.

REFERENCES CITED The following zreferences 'are of record-"in the file of this patent:

702,932 France Apr-. 21, 1931 

